On phase diagram and the pseudogap state in a linear chiral homopolymer model

Abstract

The phase structure of a homopolymer chain is investigated in terms of a universal theoretical model, designed to describe the infrared limit of slow spatial variations. The effects of chirality are studied and compared with the influence of a short-range attractive interaction between monomers, at various ambient temperature values. In the high temperature limit the homopolymer chain is in the self-avoiding random walk phase. But at low temperatures, two different phases are possible: When short-range attractive interactions dominate over chirality, the chain collapses into a space- filling conformation. But when the attractive interactions become weaker, there is a low temperature unfolding transition and the chain becomes like a straight rod. Between the high temperature and low temperature limits, several intermediate states are observed. For sufficiently high values of short-range attraction, the conventional θ-regime is observed between the self-avoiding random walk phase and the space filling collapsed phase. But when chirality increases, there is a trasition from the θ-regime to a pseudogap state. Moreover, a regime akin the θ-regime is identified between the pseudogap state, and the low temperature phase where the chain is like a straight rod. Applications to polymers and proteins, in particular collagen, are suggested.